Various braking systems designed to dissipate the kinetic energy of a vehicle are known. One such system is described in U.S. Pat. No. 5,184,875 which provides for an electronically controlled braking system. A control unit receives a braking signal from the driver. The unit selects one or more brakes of the vehicle to obtain deceleration proportional to the braking signal. The vehicle has a friction service brake and a wear-free auxiliary brake such as a fluid brake, an eddy current brake or a motor brake. Preferably, the wear-free brake is triggered and, if the braking signal is significant enough, the friction-affected brake is triggered. The system has signal transducers to detect the condition (temperature, thickness, frequency of use) of the friction-affected brake and the vehicle speed. If the system detects a condition in the brakes which has lowered their coefficient of friction, the service brake is triggered exclusively to correct the condition. If, however, the system determines that additional use of the service brakes may overheat them, it triggers the auxiliary brake additionally or exclusively.
U.S. Pat. No. 5,303,986 provides for a braking system having both an electronic pneumatic braking system and a retarder which applies a retarding torque to the vehicle driveline. The invention relates to integrating a retarder control system with a control system for the pneumatically actuated brakes to distribute the braking required between the systems without jeopardizing the braking balance between the driven and non-driven wheels. A controller receives a braking signal from the vehicle operator, from an engine or exhaust brake, or from the operator controlled retarder switches, in addition to a signal from a vehicle load sensor. The controller also receives data from sensors on each wheel regarding the speed of each wheel. The controller generates output signals to the retarder, and the engine and/or exhaust brake. During normal operation, the retarder is switched on, either manually or automatically, every time a brake application is effected. The braking signal to the drive wheels is adjusted for the effects of the retarders so that the braking balance front to rear is maintained.
U.S. Pat. No. 5,441,335 provides for an electronically controlled motor vehicle brake. An electrical braking valve pick-up generates an electrical output signal (U) as a function of the actuation path of the brake pedal and is connected to an electronic control unit. A gradient, ΔU/Δt, which represents a measure of the actuation rate of the braking value pick-up, is determined by the control unit from the variation with time of the output signal. If the gradient is above a limiting value, the unit recognizes rapid braking. The friction brake is engaged earlier and the auxiliary brake (e.g., engine brake, retarder, constant throttles) may not ever be engaged. If the gradient is below a minimum value, slow braking is present. The friction brake responds relatively late so that the slower auxiliary brake can respond first and absorb most or all of the braking need.
U.S. Pat. No. 5,613,743 provides for a method of controlling the slippage of driven wheels in a motor vehicle. Initially, a target braking torque for each of the respective driven wheels is determined. The torques are compared and the smallest of them is selected. A target engine torque is then determined from the smallest braking torque. The engine torque is adjusted to conform to the target engine torque. A residual braking torque for each wheel is calculated based upon the target engine torque and the respective target brake torques. The brake pressure at the driven wheels is varied so that the residual braking torques for each wheel are realized.
U.S. Pat. No. 5,657,838 provides for a method of operating a drive unit for a vehicle having an engine braking system. The unit has an engine, a gearbox and a retarder in a constant drive connection with the engine. The unit also has a cooling circuit where the coolant is the fluid for the retarder. The retarder acts as a pump for the cooling circuit. An overall braking output is measured and compared to a value. When the overall braking output is less than the value, the retarder is activated to deliver the required amount. When the braking output is more than the value, the engine braking system is activated along with the retarder. The retarder delivers the difference in braking between that provided by the engine braking system and required amount.
U.S. Pat. No. 5,816,665 provides for a retarder system for a drive train where the system is driven by a multi-cylinder engine via a transmission. The system has a compression brake adapted to operate in multiple stages to provide various degrees of braking to the engine. A fluid retarder, also adapted to operate in multiple stages to absorb power from the engine, is coupled for rotation with the vehicular drive train. Each stage of the retarder corresponds to a specific braking level output from the retarder. For example, stage one provides only a small amount of fluid to circulate within the retarder housing thus resulting in a small braking effect. Stage three, however, adds a predetermined amount of fluid to the retarder housing thus providing a larger braking effect. A controller is electrically connected to the compression brake and the fluid retarder to control them both to slow the speed of the vehicle.
U.S. Pat. No. 6,287,237 provides for a method of controlling a drive train including the steps of converting a braking signal from a brake petal into a braking torque. A setpoint value for an engine drag torque is determined based upon the braking torque. A downshift characteristic diagram is provided to determine a setpoint transmission ratio. The ratio is a function of the setpoint value for the engine drag torque and also of a variable functionally associated with the speed of the vehicle. The diagram has characteristic curves defined by taking into account a minimum engine torque. Lastly, a transmission ratio is automatically set by reference to the diagram.
The present invention has the advantage over the prior art by distributing the kinetic energy of the vehicle among various components of the hydrodynamic transmission based upon the actual thermal capacity of the component. Distributing the kinetic energy among the components of the transmission allows the size of the service brakes to be reduced and hence lowers their cost.